ABC reports that the rotten eggs smell in Riverside and San Bernardino is likely from the decaying Salton Sea, according to fire officials.

The outlet also suggests that change in season, shift in winds, salt from irrigation runoff, inflow of untreated water from Mexico, and the high evaporation rate of the Salton Sea -- California's largest lake, located on the San Andreas fault -- could be to blame.

Update (2:30 p.m.)

South Coast Air Quality Management District -- the air pollution control agency for Orange County and portions of Los Angeles, San Bernardino and Riverside counties -- released a statement Monday afternoon saying their inspectors were sleuthing out the origin of the stench.

Field inspectors with the South Coast Air Quality Management District are in the field today investigating possible causes of widespread sulfur odors.

Since around midnight last night, AQMD has received more than 100 calls reporting a strong, foul rotten egg/sulfur odor. Residents have complained from a very wide area including the Inland Empire and much of the Los Angeles Basin.

Fish kills, algae blooms and other biologic conditions in lakes can cause strong odors. Industrial facilities such as wastewater plants also can cause sulfur odors. At this time AQMD hasn’t confirmed any source as the cause of the widespread odor.

City News Service reports that that the smell, first noticed around 10 p.m. on Sunday, was not emanating from within Riverside, according to Chief Deputy Director for Riverside Public Utilities, Steve Badgett.

Badgett also pointed to the Salton Sea as a possible suspect in the source of the smell, noting to CNS, "We had that storm system dragging everything up from the desert yesterday, so who knows?."

Eastern Municipal Water District offcials -- servicing customers from Moreno Valley to Temecula -- said the stench was not connected to any of the district's operations.

Update (5:15 p.m.)

Throughout the day, the terrible smell has traveled a distance across Southern Califonia. A spokesman for AQMD told the L.A. Times, "It’s very unusual that any odor would be this widespread, from the Coachella to Los Angeles County...We’re talking well over 100 miles. I can’t recall ever confirming an odor traveling that distance.”